\documentclass{standalone}
\usepackage{fontspec}
\setmainfont{Source Serif 4 Variable}
\newcommand{\VF}[3]{{\addfontfeatures{RawFeature={+axis={wght=#1, opsz=#2}}}#3}}
\begin{document}
\VF{200}{60}{v}%
\VF{206}{50}{a}%
\VF{223}{39}{r}%
\VF{252}{29}{i}%
\VF{293}{18}{a}%
\VF{345}{8}{b}%
\VF{408}{8}{l}%
\VF{483}{18}{e}~
\VF{570}{29}{f}%
\VF{669}{39}{o}%
\VF{779}{50}{n}%
\VF{900}{60}{t}%
\end{document}
